1. Field of the Invention
This invention relates to an apparatus and method for reducing the transfer of vibrations between structures, that is, isolating vibration between structures. More particularly, this invention relates to an apparatus and method for reducing the transmission of vibrations between two bodies while permitting the bodies to be moved relative to one another.
2. Description of the Related Art
Many applications require that the vibrations from one body not affect another body, especially if both bodies are part of the same system. In an earth-orbiting laser system, for example, an aft body incorporating a laser cooperates with a forward body incorporating an optical projection apparatus. The laser system must be capable of (1) retargeting, that is, repositioning the forward body relative to the aft body to aim the laser at a desired target, and (2) providing quiescent tracking of the forward body relative to the aft body to maintain accurate aiming. Because of the large distance typically separating the laser from its target, very small vibratory displacements of the forward body will produce large displacements of the laser beam at the target. To maintain accuracy, vibrations must be isolated between the laser and the optical projection system during both quiescent tracking and retargeting.
In one system for isolating vibrations, disclosed in U.S. Pat. No. 3,952,979, two bodies are connected by six support members. Each support member has a central axis that intersects the central axes of two adjacent support members at right angles. Each support member also includes an accelerometer at the central axis and a coil to adjust the member's length. The accelerometers measure the respective axial components of vibrations being transferred between the bodies. These measurements are then sent to a feedback circuit that actuates the support members' coils to adjust each member's length and offset the component of the vibratory movement that corresponds to the axis of the support member. Because the bodies are mechanically connected, certain modes of vibration are transmitted between the two bodies.
Another system for vibration isolation uses magnetic actuators to support one body relative to another body by magnetic fields. Such a system is proposed by Cunningham et al. in NASA Contractor Report 3343, entitled Design of the Annular Suspension and Pointing System (ASPS) (October 1980), which is incorporated herein by reference. This system uses a plurality of magnetic actuators each having a stator connected to one body and an armature connected to the other body. The stator generates a magnetic field between a pair of spaced-apart stator cores, and the armature is suspended between the pole faces of the stator cores by the magnetic field. The magnetic fields can be adjusted to provide vibration isolation by reducing the transmission of forces between the stator and armature as one body moves relative to the other body. The magnetic actuators, however, must have very large gaps between the pole portions to permit large displacements of one body relative to the other during, for example, retargeting. Large gaps, in turn, dictate massive stators energized by large currents. The necessity for massive stators and large currents is a significant disadvantage, particularly on board earth-orbiting systems which require minimum payload weight and power consumption.
It is therefore one object of the present invention to provide a vibration isolator for efficiently reducing the transmission of vibrations between two bodies.
Another object of this invention is to provide vibration isolation between two bodies while providing for repositioning of the bodies relative to one another.
A further object of this invention is to provide a dual mode vibration isolator that permits the use of small-gap magnetic actuators of relatively low mass yet is capable of transmitting large forces while repositioning one body relative to the other.
Another object of this invention is to provide a method for isolating vibrations from transmission between a first and second body.
Additional objects and advantages of the present invention will be set forth in part in the description that follows and in part will be obvious from that description or can be learned by practice of the invention.